Internal combustion engines that rely on electronic control must have some means of sensing the various mechanical states of the engine. Consequently, numerous sensors, such as the conventional throttle position sensor, are associated with such engines, and are often located in harsh environments where temperature extremes, moisture and vibration can reduce sensor life.
The throttle position sensor provides a signal commonly used in engine control, such that it is important that means exist by which the integrity of that signal can be monitored. Evaluation of the integrity of this sensor is complicated by its indirect relationship to other engine states and by sensor output signal pollution from engine noise and system disturbances.
Techniques for checking the integrity of the throttle position sensor are in the prior art. Redundant sensors are commonly used to provide a means for sensor signal cross-verification. However, sensor tolerances can vary widely making only more expensive, precise sensors suitable for this technique. Additionally, if both sensors fail in a similar manner due to a failure in a non-redundant part of the system, they may continue to agree with each other, and the failure will go undetected. Sensor integrity can only be fully monitored by complete sensor redundancy which can add substantial cost to a system. Finally, transient signals can appear on the output signal of either sensor and may lead to an incorrect diagnosis of a fault.